This invention relates to essentially catalytically inert mineral-based particles that are adapted to be blended with particles of active cracking catalyst, particularly highly active fluidizable cracking catalysts, to adjust activity and selectivity of the particles of active catalyst to desired levels when the catalyst is used to crack oil feedstocks. The invention also relates to the manufacture of such catalytically inactive material by sintering attapulgite clay, preferably in admixture with an alkaline cementious material such as portland cement or sodium silicate.
Active fluid zeolitic cracking catalysts (FCC catalysts) are frequently utilized in oil refineries in the form of blends with fluidizable essentially catalytically inert microspheres. Reference is made to commonly assigned U.S. Pat. No. 4,493,902. The inert particles are employed to adjust activity (or activity and selectivity) of the active cracking component. Past practice was to produce the blending component by spray drying a slurry of refined kaolin clay to produce microspheres and then calcining the microspheres to dehydrate the clay. One type of inert kaolin microspheres is calcined at about 2100.degree. F.; the product typically has a BET surface area of 5-10 m.sup.2 /g and an attrition index (using the EAI procedure) of about 1%/sec. Another type of inert microspheres is calcined under more severe temperature, e.g., 2300.degree. F. and has an EAI below 1%/sec and lower surface area, e.g. below 5 m.sup.2 /g. Low surface area is a characteristic of material having low catalytic cracking activity. Reference is made to commonly assigned U.S. Pat. No. 4,781,818, especially col. 27. It has also been proposed to dilute an active cracking catalyst with a magnesium containing clay, such as attapulgite or sepiolite, for metals control during the cracking operation. See U.S. Pat. No. 4,465,779.
The manufacture of fluid cracking catalysts, including the production of blending component, utilizes premium quality refined kaolin clays and is carried out on an extensive scale. One result is a dwindling of the formerly vast reserves of kaolins. Unfortunately, kaolin clay ores are not suitable sources for the production of fluidizable blending agents without extensive wet processing steps such as degritting, particle size classification, spray drying and calcination. All of these steps, especially spray drying and calcination, are costly. The kaolin ore cannot simply be mixed with water to a plastic consistency, formed into particles by extrusion, dried, calcined and crushed to a suitable size to produce attrition-resistant blending particles.
Attapulgite type clays are naturally active, high surface area absorptive clays which normally are not interchangeable with kaolin clay. It is common practice to improve the natural absorbency of attapulgite clay by controlled crushing, extrusion, drying, milling, and similar processing. Depending upon the severity of drying, the colloidal properties of the crude clay are reduced or destroyed. Heat activated grades are adapted, among other uses, as floor cleaners and cat litters.
U.S. Pat. No. 2,665,259, assigned to a predecessor of the subject patent application, teaches that a more highly absorptive, lower bulk density and relatively hard material may be formed by compounding an attapulgite type clay, especially Georgia-Florida fuller's earth, which has not been dried to a V.M. content below 10%, with a basic cement such as portland cement. A mixture of attapulgite clay, cement and water is extruded and the extrudate is heated under relatively mild conditions such as those normally used to produce sorbent grades. Mixtures of portland cement and sodium silicate are disclosed. It has also been proposed to add a minor amount of sodium silicate to attapulgite clay to reduce the temperature at which sorptive products can be obtained. (See U.S. Pat. No. 4,339,352, commonly assigned).
Heat activated attapulgite clay has catalytic cracking activity, as would be expected from its high surface area (e.g., 60-110 m.sup.2 /g); however, the selectivity is undesirable. In U.S. Pat. No. 4,465,779 (supra) high surface area forms of clays are used as diluents. For example, the surface area of the attapulgite was 66 m.sup.2 /g and the diluent was catalytically active. While attapulgite clay is in relatively abundant supply, it is not used in present day catalyst manufacture, nor is it used to manufacture an inert binding material for use in catalytic cracking.